The latter feature I find myself using all the time. If you follow, say, a book recommendation link to the .com site, but you want to buy it on the .co.uk site. Alternatively, you may be reading a handful of reviews on the UK site, but over on the US site, there are lots more. When you’re on the Amazon.co.uk/.com site a “page action” icon will appear which, when clicked, will simply replace the amazon.co.uk in the URL with amazon.com or vice-versa.

It was incredibly simple to create. (It took longer to create the icons than write the code!) Extensions are essentially web pages that run in the background and have access to an API for interacting with Chrome: e.g. chrome.contextMenus, chrome.tabs, etc